Fix scenes reload feature to check if can do it, properly use async in play mode and ask for save if scene is modified

#1740

Source/Engine/Level/Level.cpp

@@ -1108,7 +1108,7 @@ bool LevelImpl::saveScene(Scene* scene)
 
 bool LevelImpl::saveScene(Scene* scene, const String& path)
 {
-    ASSERT(scene);
+    ASSERT(scene && EnumHasNoneFlags(scene->Flags, ObjectFlags::WasMarkedToDelete));
     auto sceneId = scene->GetID();
 
     LOG(Info, "Saving scene {0} to \'{1}\'", scene->GetName(), path);